This invention relates to communications over electrical power distribution systems and, more particularly, to a method of processing unsolicited inbound communications over such a system.
Much work has been done on two-communications systems (TWACS) by which information in the form of instructions, data, etc. is transmitted throughout an electrical power distribution network. See, for example, U.S. Pat. Nos. 5,198,796, 4,996,513, 4,963,853, 4,918,422, 4,904,995 and 4,658,238, which are assigned to the same assignee as the present invention. As is described in these patents, both outbound communications; i.e., instructional signals sent from a transmitter to a remote transponder, and inbound signals; i.e., response signals or data returned from the remote site back to the transmission point have been realized. This communication involves modulation of the power frequency voltage for outbound communications, and power frequency current modulation for inbound communications. TWACS therefore provides an infrastructure for demand side management and distribution automation.
One advantage of communications using TWACS is its ability to control time related, scheduled, operator controlled functions. These include, for example, load control, capacitor bank switching, remote reader reading, scramming, etc. Another advantage has been the ability to poll remote locations to ascertain the current operational status at the site or the surrounding points tied into that site. For example, the site may be a distribution network substation and the surrounding points stores or houses to which electricity is directed from the substation. Polling of the substation includes monitoring the status of circuit breakers to check for overload conditions, for example.
To be of use, this polling activity must be constant. However, many events at remote locations happen unpredictably. A fire at a customer's home or store, a sudden overload, emergency switching, transformer failure due to overheating, or similar events impact the distribution network. In switching, for example, a whole section of the distribution network may be disconnected and transferred from one substation to another. It would be advantageous if the TWACS were able to monitor any of these occurrences without having to poll the network at regular intervals since this would allow for better control of the network without having to be constantly on the alert for a particular condition.